सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

lagna of the moment of New Moon. Computation of the zenith-distance of the Vitribha is a little cumbrous, so that, for brevity, it is sought to compute the culminating point, obtain its declination and thereby its zenith-distance which could be taken to be the zenith-distance of the Vitribha also, from which the Nati is calculated. We are directed to obtain first the Nata or the hour angle of the Sun for the moment of New Moon. We know on that particular New Moon day how long Amāvāsya will last after Sun-rise ie. we know when the actual moment of New Moon occurs on that day. We also know the duration of day time on that day so that subtracting the time of occurence of the New Moon after Sun-rise from half the duration of day, we obtain the hour angle of the Sun (Nata) in nādis. Now the Moon's longitude is effected by parallax, the effect being depression of the Moon. It is roughly estimated that the hour angle ex- pressed in nādis is increased by ¼ of its value on account of this. Strictly speaking the effect of parallax is far more on the position of the Moon than on the Sun. But the Hindu procedure apparently treats the Sun alone for parallax. The reason is that at the moment of geocentric conjunction of the Sun and the Moon, when we consider the combined effect of parallax on the Moon and the Sun at once, for a given place, we may as well compute the relative position of the Sun effected by parallax. Let the hour-angle of the Sun in nādis be x. Then effected hour- angle will be x (1 + ¼) = 5x/4 nādis. But each Rāsi being taken roughly to rise in 5 nādis, the hour-angle in Rāsis will be 5x/4 ÷ 5 Rāsis x/4. Hence we are directed to divide the hour-angle of the Sun in nādis to divide by 4. This x/4 being substracted from the longitude of the Sun, we get the longitude of the culminating point. Then we are directed to obtain the declination of the culminating point from the formula H sin δ = H sin ω × H sin λ ÷ R,